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OKAY SO LETS LEARN SCIENCE

EXCITATION-CONTRACTION COUPLING

AN ACTION POTENTIAL TRAVELS ALONG THE MUSCLE FIBRE INTO THE SARCOLEMMA

THE ACTION POTENTIAL TRAVELS INSIDE THE SARCOLEMMA INTO THE T TUBULES

THE T TUBULES ARE SITUATED NEXT TO THE SARCOPLASMIC RETICULUM VIA A SERIES OF PROTEINS

INSIDE THE SARCOPLASMIC RETICULUM, THERE ARE TONS OF CA2+ IONS

THE ADJACENT SARCOPLASMIC RETICULUM CONNECTED TO THE T TUBULES IS CALLED A TERMINAL CISTERNAE AND THEY MAKE UP A TRIAD WITH THE T TUBULES

WHEN AN ACTION POTENTIAL TRAVELS ALONG A T TUBULE, A VOLTAGE SENSITIVE GATE OPENS AND CHANGES SHAPE CAUSING THE CALCIUM CHANNEL TO OPEN UP AND RELEASE CALCIUM TO THE SARCOPLASM

THE CROSS BRIDGE CYCLE

WITH CALCIUM IN THE SARCOPLASM, THEY CAUSE TROPONIN TO CHANGE SHAPE TO EXPOSE THE ACTIN MYOFILAMENTS

THE MYOSIN HEADS CAN BIND TO THE ACTIN MYOFILAMENTS ONLY IF IT IS ACTIVATED

IT IS ACTIVATED WHEN ATP BINDS TO THE HEAD AND IS HYDROLYSED TO ADP AND INORGANIC PHOSPHATE WHICH ARE BOTH RELEASED. THE HYDROLYSIS CAUSES THE HEAD TO ENTER INTO A COCKED POSITION AND READY TO BIND TO THE ACTIN HEAD.

ONCE ADP IS RELEASED, THE MYOSIN PIVOTS TOWARDS THE CENTRE AND THE MYOSIN HEAD ATTACHES.

THE DETACHMENT OCCURS WHEN ANOTHER ATP MOLECULE BINDS TO THE MYOSIN HEAD AND IT IS RELEASED FROM THE CROSS BRIDGE


LETS SEE BRAIN SO SYNAPSES

ACTION POTENTIALS TRAVEL ALONG THE AXON TERMINAL AND PROPAGATES THE VOLTAGE GATED CALCIUM CHANNELS TO OPEN

CALCIUM IONS ENTER INTO THE TERMINAL AND GO TO THE SYNAPTIC VESICLES WHICH RELEASE ACETYLCHOLINE

ACETYLCHOLINE BINDS TO A RECEPTOR IN THE SYNAPTIC TERMINAL AND ALLOWS THE LIGAND GATED CHANNELS TO OPEN

NA+ INFLUX, K+ EFFLUX CAUSING THE MEMBRANE POTENTIAL TO BE LESS NEGATIVE

ONCE THRESHOLD IS REACHED, ACETYLCHOLINE IS RELEASED VIA EITHER EXOCYTOSIS OR DIFFUSION AND tada


SALT CHANNELS UM UM I KNOW ABOUT THIS

NaK ATPase (or sodium pump) allows for 3Na+ to exit the basolateral membrane while allowing 2K+ into the membrane

NAK2Cl symporter allows in 2Cl-, Na+, K+ into the basolateral membrane

Cl- exits out via passive diffusion through an ion channel to the apical membrane surface to the lumen of the gut

K+ exits out via its channel

and the Na+ that enters exits via the sodium pump (which creates the force required in the first place for secondary active transport)

Cl- leaving induces paracellular Na+ and H2O fluxes